The Origin of Matter

One of the first questions for cosmologists, posed most elegantly by the Russian dissident physicist Andrei Sakharov, is: Why is there stuff? In the first moments after the big bang, it's thought that the universe was utterly empty. Shortly thereafter, matter was created—and necessarily more matter than antimatter, because otherwise the stuff and the antistuff would have annihilated each other. Cline lays out the candidates for a theory of how the fundamental particles called baryons—components of the atomic nucleus—came about. It's possible that leptons—electrons and their particle cousins—arose first, creating an asymmetry that led to the predominance of matter over antimatter.